dmaengine: tegra210-adma: Fix unused function warnings

dmaengine: tegra210-adma: Fix unused function warnings

If CONFIG_PM is not set, build warnings:

drivers/dma/tegra210-adma.c:747:12: warning: tegra_adma_runtime_resume defined but not used [-Wunused-function]
 static int tegra_adma_runtime_resume(struct device *dev)
drivers/dma/tegra210-adma.c:715:12: warning: tegra_adma_runtime_suspend defined but not used [-Wunused-function]
 static int tegra_adma_runtime_suspend(struct device *dev)

Mark the two function as __maybe_unused.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Fixes: 3145d73e69ba ("dmaengine: tegra210-adma: remove PM_CLK dependency")
Fixes: f46b195799b5 ("dmaengine: tegra-adma: Add support for Tegra210 ADMA")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/20190709083258.57112-1-yuehaibing@huawei.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>